See what a metric is worth before you save it
The Check card on a metric's page told you the definition compiles. It now also tells you the number: Run executes the metric — unsaved edits included — and shows its value over the last 30 days.
Compiling is not being right
A metric with its numerator and denominator swapped compiles. So does one whose filter excludes every row, and one that joins the wrong way round and counts each order five times. The definition is valid; the number is nonsense — and until now you found that out on a dashboard.
Run closes that gap. One click, one value, formatted exactly as the metric will appear everywhere else: 38.4%, €1,500, 1.2M. Under it, the dates actually sampled and how long the query took.
A metric whose measures have no date column to aggregate along has no period to sample, so it runs over its whole history and says All time.
Only when you ask
This is the only place in Settings → Data that queries your warehouse, so it runs on a click and never while you type. Change the definition and the value disappears rather than going stale — a number belongs to the definition that produced it. Run it again for the new one.
If the warehouse refuses the query, its own message is shown: a missing column or a permissions problem lands here instead of on someone's dashboard.